Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 20/03/2009 21:36:10
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Lorentz contraction has been mentioned a few time in threads just lately. I understand that an oblect travelling at very high speed will contract along its length in the direction of travel.
Now, GR states that if 2 objects pass each other with nothing to reference against, it is impossible for a person on 1 of them to know whether it is the object he is on or the other 1 that is moving.
So, my question is, if I was in a spaceship travelling at relativistic speed and we passed a stationary object, would it appear to me as being contracted? Surely it must to fit in with GR. But if it is velocity that causes Lorentz contraction then it wouldn't affect a stationary ship, would it?
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It is relative velocity that causes the length contraction. So the answer is yes. You would not be able to determine whether it was you or the object that was moving without some other reference. All motion is relative.
You get the same answer whether you calculate using the SR, GR, or Lorentz conventions. I like the Lorentz version because it doesn't require that we think of space and time as being distorted. All of the distortion can be attributed to the matter that moves. However, the Lorentz version is more complicated and requires a special frame of reference fixed in space.
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Thanks, Vern. I guessed it would look contracted but I wasn't sure.
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I think I can see where your thoughts went DB. Is the contraction real? And if it is a real one, and I know that I've been accelerating my ship and therefore have 'objective evidence' of me traveling very fast and then passes that other ship that, according to what we earlier agreed on, just would be standing still relative what frame of reference we both shared before this thought experiment. Will that ship be contracted 'for real' although we knew before whom it is moving faster, as we both had the same frame of reference originally (Earth).
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yor_on:
I wasn't sure whether it was due to velocity per se or relative velocity. I guessed it was relative velocity as otherwise it would contradict GR.
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Just to precise the things a little bit: the Lorentz contraction doesn't mean that the material is "compressed" as a string giving an internal tension; it's an effect only due to relativity of simultaneity:
by definition, an object's lenght is the difference of the positions of its extremes "measured simultaneously". It's for this simultaneity in the definition, that an object's lenght is frame-dependent.
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Just to precise the things a little bit: the Lorentz contraction doesn't mean that the material is "compressed" as a string giving an internal tension; it's an effect only due to relativity of simultaneity:
by definition, an object's lenght is the difference of the positions of its extremes "measured simultaneously". It's for this simultaneity in the definition, that an object's lenght is frame-dependent.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fclueless%2F1.gif&hash=ba6e884e2ac18d739c0e89967c82862b) You're trying to confuse me again. And succeeding.
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Just to precise the things a little bit: the Lorentz contraction doesn't mean that the material is "compressed" as a string giving an internal tension; it's an effect only due to relativity of simultaneity:
by definition, an object's lenght is the difference of the positions of its extremes "measured simultaneously". It's for this simultaneity in the definition, that an object's lenght is frame-dependent.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fclueless%2F1.gif&hash=ba6e884e2ac18d739c0e89967c82862b) You're trying to confuse me again. And succeeding.
[???] Think that I bieleved to clear things up!
What is unclear?
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Alberto - It's OK. I undertood it.
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There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.
In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed. Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed. However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it [;D]
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I got to admit that the question if the Lorentz contraction is a real process have been on my mind for quite some time. Those two links sees it as being as real as we see time dilation to be. http://arxiv.org/pdf/physics/0606171v1 as well as http://renshaw.teleinc.com/papers/simiee2/simiee2.stm
If it is so then I made this thought experiment wherein we have a predefined common nominator (Earth) that we start both ships from. One of them we will place being at rest with Earth, the other one will pass it accelerating to a near 'c'. They will measure each other (lasers) and will both find the other one shorter. Although we now already know that one of the ships are being at rest relative Earth and we also know that the other ship is accelerating through its creation of a 'gravity well' situated behind it we still will observe this phenomena? And it will be real?? If so,that implies that this goes for Earth to the same degree too, right?
Think now of the same system (two ships & Earth) with the exception that the formerly accelerating ship now have stopped its acceleration and are now in what we call 'uniform motion'. This mean that there is no longer any real proof of what speed or motion this ship might have, and even when looking out, there is no proof that it isn't the rest of the universe that is moving relative them instead of the other way around. But when they meet this ship again the same phenomena (Lorentz contraction) will be seen. What does this say about length? If we can't guarantee any motion as being any better than a 'preconception' based on arbitrary choices, isn't that the same as saying that our universe, depending on our choice of frame will have different sizes, also that this frame do not act only on you (accelerating ship) but also on the frame you compare it too (ship at rest versus Earth). It is a intriguing concept if it is not a optical illusion.
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Expressed as Energy one could say that the ship accelerating are collecting a lot of 'relative energy' distorting spacetime. But the ship being at rest with Earth? They will see the same effect, yet, haven't collected or received any relative energy as I understands it. To see the strangeness here you must understand that, according to those ideas, both ships length contraction is real.
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http://adsabs.harvard.edu/abs/2001APS..APR.C9001R
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There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.
In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed. Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed. However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it [;D]
Sometimes I really hate you! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fhitting%2F12.gif&hash=700b1e8e335f969537d209e0917186cb)
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There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.
In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed. Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed. However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it [;D]
Sometimes I really hate you! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fhitting%2F12.gif&hash=700b1e8e335f969537d209e0917186cb)
Noo! If you think about what I wrote, you should grasp that the paradox comes from the wrong assumption that when you measure the lenght of the ladder (or the shed) the simultaneity is absolute, while instead is frame-dependent.
Another name for this paradox is "The barn and the Pole paradox":
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
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There's a fun relativistic length-contraction thought experiment concerning a ladder and a two-doored shed.
In the thought experiment, a twelve foot long ladder is approaching an eleven foot long shed, which has a door in each end, at relativistic speed. Because of the apparent length contraction, as observed by someone standing in the shed, the observer should be able to close both shed doors while the twelve foot ladder is entirely inside the eleven foot shed. However, from the ladder's point of view, it is the shed that is contracted and it is therefore impossible for both doors to be closed while it is inside it [;D]
Sometimes I really hate you! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fhitting%2F12.gif&hash=700b1e8e335f969537d209e0917186cb)
Noo! If you think about what I wrote, you should grasp that the paradox comes from the wrong assumption that when you measure the lenght of the ladder (or the shed) the simultaneity is absolute, while instead is frame-dependent.
Another name for this paradox is "The barn and the Pole paradox":
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
ohhh, let me hit him anyway.
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Yeah, the barn and the pole is a nice example too:)
So moving/accelerating begets a shrinking universe from the frame of the one moving and for the frame 'not moving' the other ship will be the 'thing' shrinking. the first ships revelation could be explained by spacetime distortion, and what the other ships sees? Also a spacetime distortion? But if what the moving ship experience as 'shrinking' is a real effect, Then it seems to have no proportion to the energy being spent creating it. As, in fact, the whole universe reacts to this ships motion in time, and all for real. If this is true I can't help but wonder about how 'energy' transforms into 'work'.
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If work is done on an object when you transfer energy to that object, then there has been no transfer of energy as far as I can see, still the universe have shrunk as has all objects in it, the thing bugging me is that it is 'real'?
So where is this concept defining how this can be? It's not any work done on the objects outside the ships frame of reference, it's only work done on 'space' and the ship while accelerating it, and that 'work' seems to go a long way :)
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Ouch, ouch, ouch, ouch!
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If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?
[???]
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If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?
[???]
If they are traveling at a uniform velocity and being 'at rest' when compared to each other they will belong to the same 'frame of reference' and there will be no Lorentz contraction seen between them. But if you are thinking of them accelerating at the same exact velocity? I guess they still could be seen as being 'at rest'? I don't really know, that's seems a tricky one DB.
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If you were considering them as a system from another frame they should seem to close the distance between them. Edit: and as yor_on indicates, from the same frame they would see no change.
This brings to mind something that just occurred to me. As most of you now know, I prefer the Lorentz description of relativity phenomena to the Einstein version. With Lorentz, length contraction of objects in motion is a physical distortion of the objects, and not a distortion of space and time as with Einstein. So far, there has never been an experiment that could test a difference in the two concepts. So, Occam's razor cuts out Lorentz.
Now, lets apply the Lorentz version to the scenario in the OP. My near-light-speed ship is passing a stationary ship. What is my perception of the length of that stationary ship? Einstein says I see it length contracted. What about Lorentz?
It seems now as I think about it, the Lorentz version where my measuring devices suffer the contractions, and the stationary ship does not, Lorentz should say the stationary ship seems expanded, not contracted.
There is a proposed test of this by a satellite containing a very precise measuring device that can measure the angle between two stars. The test proposal is that the speed of the earth in orbit is enough to change the apparent angle between two stars from one earth season to the next. If my thinking is right, the Einstein version would see the contraction. The Lorentz version should see no contraction.
The reason why is: Half of the effect is due to aberration, the other half, contraction due to earth's motion relative to the stars. Aberration and contraction are additive so produce double the calculated contraction with Einstein. Aberration and Lorentz expansion would cancel, so that no effect would be seen.
Edit: That last sentence should read: Aberration and apparent expansion due to Lorentz contraction of local measuring devices would cancel ....
Here's a link to the article about the test. (http://renshaw.teleinc.com/papers/rs98-sim/rs98-sim.stm)
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If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?
[???]
If they are traveling at a uniform velocity and being 'at rest' when compared to each other they will belong to the same 'frame of reference' and there will be no Lorentz contraction seen between them. But if you are thinking of them accelerating at the same exact velocity? I guess they still could be seen as being 'at rest'? I don't really know, that's seems a tricky one DB.
I meant to an outside observer.
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Vern, when I read him I got the impression that he accepted length contraction as real, reading him again I see that he seem to doubt it by his conclusive words? But there is still the muon test wherein he writes "In the muon's’ frame of reference, the situation is quite different. The only way this can happen in the muon's’ reference frame is if the actual physical distance that must be traveled by them is shortened as in (8). This is not a visual effect for the muon. If the distance traveled by the muon is not physically shorter, the muon simply does not remain in existence long enough to make the trip, even at speeds greater than .9c. To the muon, length contraction is clearly not merely a visual effect, as the muon is not "seeing" anything. The distance to be traveled by the muon from the upper atmosphere to sea level is physically shorter than the same distance measured by a slower moving particle. The high speed muon performs Einstein’s train embankment experiment first hand."
I don't really know what to think here, in what way do you mean that this aberration cancels out Lorentz contraction? It seems to go both ways depending on the observer? ". The maximum amount of the aberrational displacement of a star is approximately 20 arcseconds in right ascension or declination. ".It seems to depend on the movement relative the observer? Or am I thinking wrong here?? http://en.wikipedia.org/wiki/Aberration_of_light#Apparent_and_true_positions
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Ok DB, got it.
And again, I don't know :)
The difficulty here seems to be to decide what the 'system' observed consists of. Is it only the material objects that we will observe this phenomena on or should space between them be included. If one consider the 'muon description' it definitely seem to consider 'distance' in itself so considering this I would expect it to have an effect on the space surrounding those two objects. Even if space is 'empty' of matter it still can contain a 'distance', but is that space moving? Shouldn't it be seen the same way as the observer? as relative the moving ship containing non moving 'static points' in spacetime? This one is sooo strange to me :) Lightarrow et al, give it a shot. There is definitely at least two 'camps' of reasoning here, if not more?? http://www.physicsforums.com/showthread.php?t=106526 and no one seems totally 'wrong'. The muon example seems like a reasonable proof to me as we have proofs for time dilation and this one, according to what I understands (not much:), is similar..
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Hi yor_on; I agree that Curt Renshaw, in the link, has some notions about the cause of the Lorentz contraction that is at odds with what most of us suspect. But he does describe the proposed experiment that would see a difference between the Lorentz version of space-time and the Einstein version IMHO.
Yes; the muon must see the distance shortened as well as the time dilated in order to reach the earth's surface as a muon. I haven't thought about this enough to understand if it rules out the Lorentz version.
The referenced experiment was supposed to take place in 2005. I wonder what the results indicated. A positive result would support the Einstein version, a negative result would support the Lorentz version -- but it wouldn't rule out Renshaw either.
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I have a link saying that the experiment should start 2008.
http://adsabs.harvard.edu/abs/2001APS..APR.C9001R but I've found no conclusions drawn from it on the 'net yet' njet :)) : (<--- Lorentz contracted smiley:)
I've such a bad sense of humor..
My doctor told me it was to late to cure too.
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Thanks for the link yor_on. If it did start in 2008, someone should have results by now. But this in one of those cases where a positive result would be announced right away. A negative result may never be reported [:)]
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If 2 objects are following each other at relativistic speed then the distance between the front and back of each object appears to shrink. So what about the distance between the back of the first object and the front of the second? Does that also appear to shrink so that they seem closer together?
[???]
Of course.
If you travelled at very high speed(*), you would measure all distances between points (which are moving with respect to you) as contracted, independently where those points are (in matter or in the void). At very high speed, not only you would measure all bodies, example planets and stars, as "compressed" in dishes, but also theire distances would be so. In a few seconds (or more or less, according to your speed) you could travel along all the universe.
(*)Of course the same if bodies travelled and you were still, there is no difference, what counts is relative motion.
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You've touched on what I was wondering. Would that be a way for us to see what is outside our visible universe? If we were travelling at relativistic speed, the distance between us and the visible horizon would be less. Does the contraction mean we could see past it or would time dilation rear its ugly head and prevent it?
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You've touched on what I was wondering. Would that be a way for us to see what is outside our visible universe?
Certainly, you would be able to go everywhere in the existing universe, visible or not.If we were travelling at relativistic speed, the distance between us and the visible horizon would be less. Does the contraction mean we could see past it or would time dilation rear its ugly head and prevent it?
The lenght contraction means that you could arrive there in a few seconds, and, furthermore, that light from a distant source beyond the limit will have to cover a less distance to reach us, but we couldn't see past it from the beginning, we should wait to meet the light (emitted from the distant source) at ~ half journey.
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Thank you, Alberto.
Is there a limit to the amount of contraction or is it another 1 of those horrible infinity things? At c, does everything have zero length?
You see, there was another side to this that I was wondering about and that's why I mentioned time dilation. If you could travel at, say, 0.99c, how much contraction would there be between you and the horizon of the visible universe? Or does contraction only apply when you pass someting?
Here's what I was puzzling over. In our frame of reference here on Earth it has taken light 13.7 billion years to get here. Now, nothing can travel faster than c and in your own frame of reference it doesn't matter how fast you go, time will appear to pass at the normal rate. So, it should take you more than 13.7 billion years to get there by your own timescale. But, if the distance is greatly contracted then at 0.99c it may take you less than 13.7 billion years to get there. That can't be right.
The only solution I can see is that time dilation must come into it somehow but I can't figure out how because in your own frame of reference there shouldn't be any. Or is there something else that I'm missing completely?
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Thank you, Alberto.
Is there a limit to the amount of contraction or is it another 1 of those horrible infinity things? At c, does everything have zero length?
Yes.
You see, there was another side to this that I was wondering about and that's why I mentioned time dilation. If you could travel at, say, 0.99c, how much contraction would there be between you and the horizon of the visible universe?
Sqrt(1 - 0.992) ~ 0.14, so 1km --> 0.14km.
Or does contraction only apply when you pass someting?
No, always.
Here's what I was puzzling over. In our frame of reference here on Earth it has taken light 13.7 billion years to get here. Now, nothing can travel faster than c and in your own frame of reference it doesn't matter how fast you go, time will appear to pass at the normal rate. So, it should take you more than 13.7 billion years to get there by your own timescale.
Haven't understood this one.
But, if the distance is greatly contracted then at 0.99c it may take you less than 13.7 billion years to get there. That can't be right.
Why? You get there in 13.7*0.14 = 1.92 billion years.
If you want to get there in 1 year (for example), you should travel at:
0,9999999999999999999999733603282c.
The only solution I can see is that time dilation must come into it somehow but I can't figure out how because in your own frame of reference there shouldn't be any. Or is there something else that I'm missing completely?
Can't grasp your actual concern.
Edit: I made a slight mistake in my previos computation of the time you need to get there; actually is 1.92/0.99 = 1.94 billion years.
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... in your own frame of reference it doesn't matter how fast you go, time will appear to pass at the normal rate.
Consider what this actually means. What would you expect to see if this was not true?
You can look out to other frames of reference and see them running fast or slow by your watch, but time is always going to be uniform in your own frame of reference, so it can only run fast or slow relative to another frame. You will always see your watch running at the same rate, whatever happens, because if time slows or speeds up (relative to an external frame) for your watch, it slows or speeds up for everything else in your reference frame, including your physiology, the operation of your brain, etc.
If that's not what you meant, I'm curious to know what you did mean.
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dlorde - That is precisely my point.
Alberto - You said "You get there in 13.7*0.14 = 1.92 billion years.".
From the point of view of someone on Earth, it has taken light 13.7 billion years to make the journey. From the perspective of someone travelling at 0.99c light would still be travelling at c relative to him (basic GR). Therefore, to him light would still take 13.7 billion years to travel that same distance. Am I right so far?
If so, then it follows that he cannot possibly cover the same distance in 1.92 billion years in his own frame of reference. To do so he must travel at 13.7/1.92 = 7.14c. How does that resolve?
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dlorde - That is precisely my point.
Alberto - You said "You get there in 13.7*0.14 = 1.92 billion years.".
From the point of view of someone on Earth, it has taken light 13.7 billion years to make the journey. From the perspective of someone travelling at 0.99c light would still be travelling at c relative to him (basic GR). Therefore, to him light would still take 13.7 billion years to travel that same distance. Am I right so far?
No, because the distance is smaller. Let's say that at 13.7 billion light years (limit of visible universe) there is a quasar which name is "Q" and that from there a beam of laser light is sent in direction Earth at the moment of your passing close to Earth, in direction Q, with your starship, at 0.99c. Inside your starship you measure as distance from you and Q: 1.92 billion light years. How long will something travelling at c take to reach you? time = space/velocity = 1.92 billion light years/c = 1.92 billion years, so you would receive the beam of laser light in 1.92 billion years.
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So if you were travelling at 0.99c the light from the edge of the visible universe would take considerably less than 13.7 billion years to reach Earth? The visible edge would no longer be 13.7 billion years * 300,000km/sec distant?
How far does the contraction go? From the photon's perspective, would the distance be zero?
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So if you were travelling at 0.99c the light from the edge of the visible universe would take considerably less than 13.7 billion years to reach Earth?
No, to reach *you*.
The visible edge would no longer be 13.7 billion years * 300,000km/sec distant?
You should have written 13.7 billion years * 1 light year/year = 13.7 billion light years, however it wouldn't be that distance anylonger *for you*; for Earth would be the same.
How far does the contraction go? From the photon's perspective, would the distance be zero?
The photon's perspective doesn't exist. Let's talk about the perspective of a passenger travelling at near c: yes.
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So if you were travelling at 0.99c the light from the edge of the visible universe would take considerably less than 13.7 billion years to reach Earth?
No, to reach *you*.
But, surely, you would see the distance between the edge and Earth contracted therefore light would travel that distance in less than 13.7 billion years.
How far does the contraction go? From the photon's perspective, would the distance be zero?
The photon's perspective doesn't exist. Let's talk about the perspective of a passenger travelling at near c: yes.
My brain is going to hurt again now. I just know it.
OK. So at (near)c distance reduces to zero. Therefore it must take zero time to get anywhere as everywhere would be in the same place but of zero length. That sounds like a singularity to me [???]
Would you yourself be contracted to zero size? If not, how could you fit there? And if it is only length that is contracted, does that mean that everything becomes 2-dimensional? I don't like the thought of that.
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No, to reach *you*.
But, surely, you would see the distance between the edge and Earth contracted therefore light would travel that distance in less than 13.7 billion years.
Yes, but while *in your frame of reference* light will meet Earth in 1.92 b.y., *in the Earth frame* it'll be 13.7 b.y.
The photon's perspective doesn't exist. Let's talk about the perspective of a passenger travelling at near c: yes.
My brain is going to hurt again now. I just know it.
OK. So at (near)c distance reduces to zero. Therefore it must take zero time to get anywhere as everywhere would be in the same place but of zero length. That sounds like a singularity to me [???]
Infact it's even for this reason that the photon's perspective doesn't exist [:)]. If you talk about "near c", instead, then distances and time intervals of travels are not zero, even if as little as you want, approaching c.
Would you yourself be contracted to zero size?
You wish it was! [;)]. Apart from jokes, from your frame of reference in the starship, everything and of course everyone moving with respect to you would be contracted, not yourself (but you would be contracted *for them*).
If not, how could you fit there? And if it is only length that is contracted, does that mean that everything becomes 2-dimensional? I don't like the thought of that.
Yes, the "thickness" in the direction of movement would tend to reduce to zero so everything would become bidimensional. You don't like it? But do you realize that you need almost an infinite amount of energy to reach almost c? It's not just to push on the accelerator...
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The thought I don't like is that dimensions can be reduced to zero size by velocity. What does that say about our concept of dimensions? Or time, for that matter?
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In fact that is one of the most confusing truths I know of Lightarrow:)
And a very nice description/discussion btw.
We know that a photon at all times moves at 'c' (depending on density:)
We also know that it has a 'duality' (light 'matter')
Therefore, from the perspective of that photon, on one hand I could say that it both encompass all 'time' there ever has been, as well as say, ah, on the other hand, that it has no 'time' at all as it doesn't really exist in 'time'. Encompass all 'time' as that very first one, if seen as a particle :) would should and will see our universe die, or rather, not even notice it at all from its birth to its death. I love it ::))
On the third hand though :) it's photons that interact with us all, from the ones showing of 'at' our atoms to the ones we can see ((you've already heard that we can see a photon I presume :) Is that a true statement btw?:)
And it's this last remarkable ability that really freaks me 'off' and on...
That they can 'interact' in time I mean, not that we might be able to see one with our eyes.
Anyway you look at it, and I have looked at it :), I still having trouble reconcile myself with its 'ability' to interact in 'time' while in itself more or less, to my eyes that is, existing 'outside' of it.
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If you like, thinking of that very first photon coming into 'existence' you could ask yourself if there could exist any more photons as seen from the perspective of that first one, where would they take 'place'?
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And it's this last remarkable ability that really freaks me 'off' and on...
That they can 'interact' in time I mean, not that we might be able to see one with our eyes.
Anyway you look at it, and I have looked at it :), I still having trouble reconcile myself with its 'ability' to interact in 'time' while in itself more or less, to my eyes that is, existing 'outside' of it.
Which is something I was getting to. I was taking it 1 step at a time to make sure I was thinking correctly.
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Ouch DB, sorry, my only defense would be that the questions you state are similar to my own:)
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The thought I don't like is that dimensions can be reduced to zero size by velocity. What does that say about our concept of dimensions? Or time, for that matter?
It's only a mathematical limit, you will never be able to reach exactly c, so why do you worry about it exactly?
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And it's this last remarkable ability that really freaks me 'off' and on...
That they can 'interact' in time I mean, not that we might be able to see one with our eyes.
Anyway you look at it, and I have looked at it :), I still having trouble reconcile myself with its 'ability' to interact in 'time' while in itself more or less, to my eyes that is, existing 'outside' of it.
Which is something I was getting to. I was taking it 1 step at a time to make sure I was thinking correctly.
One possible way of interpreting it is that what we view as the photon's movement through space seems, to the photon, to be it's movement through time; the photon doesn't think it's moving through space at all but believes it's stationary (that's if a photon were to have any awareness, of course).
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The thought I don't like is that dimensions can be reduced to zero size by velocity. What does that say about our concept of dimensions? Or time, for that matter?
It's only a mathematical limit, you will never be able to reach exactly c, so why do you worry about it exactly?
OK, forget zero size. Their effective size can be altered by velocity. I find that troublesome.
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OK, forget zero size. Their effective size can be altered by velocity. I find that troublesome.
Why?
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I just don't like the thought of it. It just seems wrong. I want to punch it.
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I just don't like the thought of it. It just seems wrong. I want to punch it.
What is "wrong" it to ascribe essential meanings to the concepts of "space" and "time"; they haven't.
(But we were born with them so it's difficult for us humans to get rid of them).
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What is "wrong" it to ascribe essential meanings to the concepts of "space" and "time"; they haven't.
(But we were born with them so it's difficult for us humans to get rid of them).
It's not that it's difficult for me to accept that space & time are not rigid structures. I understand warping & contraction of space, and its implications, due to gravity. My problem is getting to grips with the notion that distances can get shorter as we move faster. I know the difference would be immeasurably small, but if I walk somewhere it will be further than if I drive there at 100mph.
I fully accept time dilation and I don't have a problem with that as I more-or-less understand the reasoning behind it. But I don't understand contraction of distance in the same way. Maybe if I did I would feel happier about it.
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What is "wrong" it to ascribe essential meanings to the concepts of "space" and "time"; they haven't.
(But we were born with them so it's difficult for us humans to get rid of them).
It's not that it's difficult for me to accept that space & time are not rigid structures. I understand warping & contraction of space, and its implications, due to gravity. My problem is getting to grips with the notion that distances can get shorter as we move faster. I know the difference would be immeasurably small, but if I walk somewhere it will be further than if I drive there at 100mph.
I fully accept time dilation and I don't have a problem with that as I more-or-less understand the reasoning behind it. But I don't understand contraction of distance in the same way. Maybe if I did I would feel happier about it.
As i tried to explain (probably I didn't succeed [:)]) it's not a "real" contraction in the sense that there is no internal tension; you could think of it as an "artefact" of how we *define* distance between two points: you have to measure the two points positions *simultaneously*. To do this, the points have to send their position information to the experimenter, and this is done with light, which has not an infinite speed, so these informations don't arrive simultaneously to a moving experimenter, if they arrive simultaneously to an experimenter at rest. For this reason their distance is not the same anylonger. Don't know if you now grasped something.
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Alberto - I'm just getting more confused now.
Look at this quote:
The lenght contraction means that you could arrive there in a few seconds, and, furthermore, that light from a distant source beyond the limit will have to cover a less distance to reach us, but we couldn't see past it from the beginning, we should wait to meet the light (emitted from the distant source) at ~ half journey.
Your reply states (where I've highlighted it) that the distance would be less yet now you are saying that it is the way that distance is measured that makes it seem less:
it's not a "real" contraction in the sense that there is no internal tension; you could think of it as an "artefact" of how we *define* distance between two points
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I just don't like the thought of it. It just seems wrong. I want to punch it.
Lol
Try thinking in terms of that summed-vector view I've mentioned in a couple of threads. In that interpretation, everything is always traveling at 'c'. However, that constant speed of 'c' is a sum of two vectors and while the product of the two vectors is an absolute, the individual vectors, representing space and time, aren't. Space and time then, can be any value, as long as they sum to the absolute value 'c'. I think that what makes this counter-intuitive is that it seems the other way around to us; it is space and time that appear to be constant, which it is, but only from our point of view, which is dictated by the summed vector.
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Alberto - I'm just getting more confused now.
Look at this quote:
The lenght contraction means that you could arrive there in a few seconds, and, furthermore, that light from a distant source beyond the limit will have to cover a less distance to reach us, but we couldn't see past it from the beginning, we should wait to meet the light (emitted from the distant source) at ~ half journey.
Your reply states (where I've highlighted it) that the distance would be less yet now you are saying that it is the way that distance is measured that makes it seem less:
it's not a "real" contraction in the sense that there is no internal tension; you could think of it as an "artefact" of how we *define* distance between two points
I put the word "artefact" in commas because it's not a real artefact, but the reality; Writing that way I just wanted to point out that it's a relativistic effect, that is it's due to how we define distance, which depends on the frame of reference. Maybe it's this that you aren't grasping: our definition of distance is frame-dependent, it's not an *intrinsic* property of bodies or of space.
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Alberto - I'm just getting more confused now.
Look at this quote:
The lenght contraction means that you could arrive there in a few seconds, and, furthermore, that light from a distant source beyond the limit will have to cover a less distance to reach us, but we couldn't see past it from the beginning, we should wait to meet the light (emitted from the distant source) at ~ half journey.
Your reply states (where I've highlighted it) that the distance would be less yet now you are saying that it is the way that distance is measured that makes it seem less:
it's not a "real" contraction in the sense that there is no internal tension; you could think of it as an "artefact" of how we *define* distance between two points
I put the word "artefact" in commas because it's not a real artefact, but the reality; Writing that way I just wanted to point out that it's a relativistic effect, that is it's due to how we define distance, which depends on the frame of reference. Maybe it's this that you aren't grasping: our definition of distance is frame-dependent, it's not an *intrinsic* property of bodies or of space.
I want my mummy! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fcrying%2F2.gif&hash=6f40ed49d250203da654520072aa4687)
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Let me go away & have a think.
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I want my mummy! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Fcrying%2F2.gif&hash=6f40ed49d250203da654520072aa4687)
I always loved the Rolf Harris version of that song [:D]
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If 'distance' is a property of 'frames', where are we?
Once 'we' were an idea inside a cave looking out. Now we are 'out' of that cave, but we still need to define what 'distance' is. If we can't define 'rest', and can't define 'distance', as anything more than a relation between 'two frames of reference' we shouldn't expect space to have any recognizable' property's except those we need to define ourselves in it :) And that, in fact, just create the same dilemma as when we once saw the the sun as movóng around us.
So, what conclusions can we draw from this statement? Only this, that what we can test by repeatable experiments under controllable circumstances will be the 'inclinations' toward what spacetime possibly is. That doesn't say that we can't speculate, it just mean that spacetime seems like something not applicable to Newtonian standards, and that means those 'standards' that we see as applying 'locally' macroscopically for us.
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So, what conclusions can we draw from this statement? Only this, that what we can test by repeatable experiments under controllable circumstances will be the 'inclinations' toward what spacetime possibly is.
IMHO this is about as close as we can get to reality. We can measure and guess. And if we continue as in the past; we will guess wrong the first few times. [:)]
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I would define 'distance' as: The measure of difference between two values.
The actual distance measured can be dependent upon upon your frame of reference though, so two different frames of reference may measure two different distances.
I think that part of the problem we're discussing is that it's impossible to measure what we're trying to measure in the way that we're trying to measure it. For example, if we measured the length of something in terms of the angular difference between it's two ends, it's length would vary according to how far away it was from us; "These are small... but the ones out there are far away. Small... far away... ah forget it!" - Father Ted
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"These are small... but the ones out there are far away. Small... far away... ah forget it!" - Father Ted
Classic! [:D]
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I would define 'distance' as: The measure of difference between two values.
...of positions, measured *simultaneously*.
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I'm still wrestling with the concept of Lorentz space-time vs Einstein's SR. Now I see how the length of a stationary object must be contracted when moving past it even with the Lorentz version. I forgot that time is also dilated for the moving vessel. That means it would pass the stationary vessel in less time, and so would measure its length as contracted. So the situation is the same.
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I would define 'distance' as: The measure of difference between two values.
...of positions, measured *simultaneously*.
Ah - no. In any measurement, a difference is a difference. And that's what it really comes down to; we can move stuff around, to make the difference look different, from different points of view, but at the end of the day there's a difference that needs to be accounted for. You can't just shrug it off as imaginary.
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That is the 'funny' thing about it, ain't it? It's a 'difference of positions, measured simultaneously.' we are used to see 'distance' as something needing only one observer to be 'true'. LeeE described 'father Ted' here :)
Still, that ain't the whole 'truth' as i see it, as long as we have a 'depth perspective' to measure something in we trust in that, what I see and what you see, if different, will be explainable as consisting of being measured from different distances. But that has nothing to do with Lorentz contraction as I see it.
If it is a 'real' situation with length being dependent on the relative motion as measured between two 'frames of reference' then distance is a questionable thing to me.
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Perspective only works in flat space.
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I would define 'distance' as: The measure of difference between two values.
...of positions, measured *simultaneously*.
Ah - no. In any measurement, a difference is a difference. And that's what it really comes down to; we can move stuff around, to make the difference look different, from different points of view, but at the end of the day there's a difference that needs to be accounted for. You can't just shrug it off as imaginary.
Sorry, but I haven't grasped what you mean.
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Just me thinking of the analogue with 'father Ted' :)
I see Lorenz contraction as something different than angular problems of distance. To me it questions the whole idea of 'distance' whatsoever if it is real.
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What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.
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You introduce a interesting question there Lightarrow.
Can one isolate f ex. time from 'spacetime' and say that it is time that change the measurements?
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What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.
Spatial distance can be defined without needing to reference temporal distance. In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining. For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time. However, it may measured as being a different length depending on the frame of the measuring observer.
The difference between the observed relativistic temporal and spatial effects when such an object closely approaches a BH and then returns to a distant observer are that the spatial length can be reconciled but the temporal durations can't i.e. the ruler is the same length as it was before, but it's now younger than the observer. Hmm... have I crossed topics here?
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What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.
Spatial distance can be defined without needing to reference temporal distance. In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining. For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time. However, it may measured as being a different length depending on the frame of the measuring observer.
As to say: "it's red, unless it isn't" [:)]
To define distance you have to measure positions of points at specific times; imagine a spring which is slowly extending: now it's 1 metre long, after 1 hour is 1.001 metres, ecc. Which is its lenght? You can't avoid using the concept of time.
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Some statements, you tell me if and where you disagree :)
The universe have general macroscopic properties as 'Time' and three 'spatial dimensions'. Inside them we find matter and vacuum and light. Matter and vacuum (space) are defined in/as density and distance. A perfect vacuum is defined as containing no matter nor mass nor density. Distance is defined as being a property relating to what frames of reference we use to compare and measure it with.
Light is measured as a invariant velocity in a vacuum over a certain distance in time. It is also thought to consist of 'light quanta' of a invariant energy amount. Light will always be 'time less' no matter how much it is 'slowed down' as seen from another frame of reference. It is also seen as a 'duality' in that we have experiments proving it to act as a particle as well as waves. Photons in QED (Quantum Electro Dynamics) are seen as both 'real' photons existing in a continuum in measurable time (Sun Earth) and as 'virtual' photons 'surrounding' atoms and outside measurable time.
Those virtual photons is expected to be responsible for the forces of electricity and magnetism. and also (?) seem to be the carriers of all other 'communication' between particles? A perfect Vacuum, although empty of 'matter', have a hidden 'energy' as well as consisting of virtual particles. Those interact with our macroscopic spacetime although they themselves are of to short duration to become measurable according to HUP (Heisenberg's Uncertainty Principle) and Planck time. So what do we have?
Light/photons/waves acting in a twofold manner, as measurable light and as unmeasurable light, 'timeless' internally but obeying spacetimes geodesics and able to act 'in time' on our universe, existing as a needful property for both living as well as dead matter. A vacuum devoid of matter (if perfect) but not of energy and virtual particles, and also containing 'distances'. Matter which I 'split' in two parts, 'living' and 'dead'.
So what else have I forgotten here?
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What I mean is that it's impossible to define "distance" without using the concept of time, and time, we now know, is frame-dependent.
Spatial distance can be defined without needing to reference temporal distance. In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining. For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time. However, it may measured as being a different length depending on the frame of the measuring observer.
As to say: "it's red, unless it isn't" [:)]
To define distance you have to measure positions of points at specific times; imagine a spring which is slowly extending: now it's 1 metre long, after 1 hour is 1.001 metres, ecc. Which is its lenght? You can't avoid using the concept of time.
I can't quite see what point you're trying to make here.
You've quoted me as saying "Spatial distance can be defined without needing to reference temporal distance. In practical terms, we can't measure a spatial distance because we need time within which to function, but measuring isn't the same as defining", which I thought made the difference between defining and measuring pretty clear, but then you say "To define distance you have to measure positions of points at specific times", which is just plain incorrect; you can define something without needing to measure it. If I define something to be 30cm long then measuring it is redundant - it is by definition 30cm long.
I also don't understand why you've also highlighted the next bit of text where I say "For example, consider a 30 cm long rule; unless something happens to change that rule, it will always be 30 cm long and that distance will not vary over time" and then go on to talk about a spring that is explicitly changing over time: how is it relevant to compare something that explicitly doesn't change over time with something that explicitly does?
You can't avoid using the concept of time
The concept of time? Well, I guess that with something that doesn't change over time, the concept of time is relevant, but only by virtue of time being specifically excluded as a factor.
When a state changes, yes, time is a factor, but where there is no change of state time is not a factor because the state is constant and there is no change of state over time; any formula that tries to link the state S with time t isn't going to work because a change in t is not reflected by a change in S. Indeed, in any such formula, t must be meaningless for any value of t if S is to remain unchanged.
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Can you *define* a spatial distance to be 30 cm long, without having to make a measurement? Are you talking about physics or about philosophy?
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Can you *define* a spatial distance to be 30 cm long, without having to make a measurement? Are you talking about physics or about philosophy?
Physics is a sub-set of philosophy and at the level we're discussing physics, dealing with abstracts is part of the deal. Are you discussing engineering or physics?
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Can you *define* a spatial distance to be 30 cm long, without having to make a measurement? Are you talking about physics or about philosophy?
Physics is a sub-set of philosophy and at the level we're discussing physics, dealing with abstracts is part of the deal. Are you discussing engineering or physics?
Can you show me a (serious) book of physics where it's written that you can *define* a distance between two points without having to measure it, apart the sample metre, of course?
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Some statements, you tell me if and where you disagree :)
The universe have general macroscopic properties as 'Time' and three 'spatial dimensions'. Inside them we find matter and vacuum and light. Matter and vacuum (space) are defined in/as density and distance. A perfect vacuum is defined as containing no matter nor mass nor density. Distance is defined as being a property relating to what frames of reference we use to compare and measure it with.
Light is measured as a invariant velocity in a vacuum over a certain distance in time. It is also thought to consist of 'light quanta' of a invariant energy amount. Light will always be 'time less' no matter how much it is 'slowed down' as seen from another frame of reference. It is also seen as a 'duality' in that we have experiments proving it to act as a particle as well as waves.
I essentially agree up to here.
Photons in QED (Quantum Electro Dynamics) are seen as both 'real' photons existing in a continuum in measurable time (Sun Earth) and as 'virtual' photons 'surrounding' atoms and outside measurable time.
Many people says virtual particles are nothing more than a mathematical tool in quantum fields theory and so we shouldn't think of them as really existing.
Those virtual photons is expected to be responsible for the forces of electricity and magnetism. and also (?) seem to be the carriers of all other 'communication' between particles? A perfect Vacuum, although empty of 'matter', have a hidden 'energy' as well as consisting of virtual particles. Those interact with our macroscopic spacetime although they themselves are of to short duration to become measurable according to HUP (Heisenberg's Uncertainty Principle) and Planck time.
The problem is not much of HUP but of the fact that virtual particles are "out of shell" that is don't obey E2 = (mc2)2 + (cp)2
So what do we have?
Light/photons/waves acting in a twofold manner, as measurable light and as unmeasurable light, 'timeless' internally but obeying spacetimes geodesics and able to act 'in time' on our universe, existing as a needful property for both living as well as dead matter. A vacuum devoid of matter (if perfect) but not of energy and virtual particles, and also containing 'distances'. Matter which I 'split' in two parts, 'living' and 'dead'.
So what else have I forgotten here?
Billions of things that we'll discover in the (near or far) future... [:)]
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Many people says virtual particles are nothing more than a mathematical tool in quantum fields theory and so we shouldn't think of them as really existing.
I think this is a very good observation and predict that it will eventually be the accepted hypothesis.
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Lightarrow, when I write "Those interact with our macroscopic spacetime although they themselves are of to short duration to become measurable according to HUP (Heisenberg's Uncertainty Principle) and Planck time." you say that it hasn't to do with HUP? They are as you say 'out of shell', if you by that mean 'virtual', not being 'consistent in time'? To me it is HUP that best describes it, that and them possibly being 'under' Planck's definitions.
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Lightarrow, when I write "Those interact with our macroscopic spacetime although they themselves are of to short duration to become measurable according to HUP (Heisenberg's Uncertainty Principle) and Planck time." you say that it hasn't to do with HUP? They are as you say 'out of shell', if you by that mean 'virtual', not being 'consistent in time'? To me it is HUP that best describes it, that and them possibly being 'under' Planck's definitions.
Virtual particles are not such because they have a too short life, but because they don't obey the equation I wrote in my previous post. It's theyr existence which is allowed by HUP; the property of "being virtual" is "not-obeying that equation".
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That one you will have to go into in more detail to make me see Lightarrow? I'm not saying that HUP is the reason for them existing btw, I'm just finding it a 'best explanation' for how they might exist, and exist they seem to do, even if we just have 'indirect evidence' for them:)
But then again, if they're outside observable time, how would we observe them?
Then again, I do have another view of how it might work, but that one is so outlandish that I'll wait with it :)
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That one you will have to go into in more detail to make me see Lightarrow? I'm not saying that HUP is the reason for them existing btw, I'm just finding it a 'best explanation' for how they might exist, and exist they seem to do, even if we just have 'indirect evidence' for them:)
Yes, but that 'indirect evidence' comes from a *specific* way of computing things: perturbation theory, which is only a tool in making approximate computations in QFT, because we still don'y know how to make the complete non-approximate computations; it could come out that virtual particles are not needed at all if we were able to make the complete computation; infact QFT actually treats quantized *fields*, not particles; it's that quantization what we usually call "particles".
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I found this wiki article that expands on QFT and is in agreement with lightarrow's comments. The last sentence in the quote below gives the reason a virtual particle can never be detected.
cannot be detected while carrying the force, because such detection will imply that the force is not being carried.
From Wiki (http://en.wikipedia.org/wiki/Quantum_field_theory)
In quantum field theory (QFT) the forces between particles are mediated by other particles. For instance, the electromagnetic force between two electrons is caused by an exchange of photons. But quantum field theory applies to all fundamental forces. Intermediate vector bosons mediate the weak force, gluons mediate the strong force, and gravitons mediate the gravitational force. These force-carrying particles are virtual particles and, by definition, cannot be detected while carrying the force, because such detection will imply that the force is not being carried.
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That one you will have to go into in more detail to make me see Lightarrow? I'm not saying that HUP is the reason for them existing btw, I'm just finding it a 'best explanation' for how they might exist, and exist they seem to do, even if we just have 'indirect evidence' for them:)
Yes, but that 'indirect evidence' comes from a *specific* way of computing things: perturbation theory, which is only a tool in making approximate computations in QFT, because we still don'y know how to make the complete non-approximate computations; it could come out that virtual particles are not needed at all if we were able to make the complete computation; infact QFT actually treats quantized *fields*, not particles; it's that quantization what we usually call "particles".
What I'm having problems with is 'renormalization' :)
And that idea I've had problem since I first saw it Lightarrow:)
And now you say I will have problems with perturbation theory as well
And quantum field theory too??
Lightarrow, do you remember how dissatisfied I am with my understanding of distance:) If distance is something relating, and only relating, to 'frames' observing 'frames', what is uniform motion, speed, velocity, acceleration? And what the heck is a 'direction'?
And perhaps most importantly, what is time?
We seem to describe things from a format where we expect numbers to come up the same, but our universe seems more likely to conform to a 'sliding standard', where things don't come up the same. Like the way time seems to act in QM as compared to our macroscopic universe. When we 'renormalizes' something we expect it to behave in a accountable manner with a clear 'causality chain' showing from the least to the biggest. Now, isn't that a preconception?
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That one you will have to go into in more detail to make me see Lightarrow? I'm not saying that HUP is the reason for them existing btw, I'm just finding it a 'best explanation' for how they might exist, and exist they seem to do, even if we just have 'indirect evidence' for them:)
Yes, but that 'indirect evidence' comes from a *specific* way of computing things: perturbation theory, which is only a tool in making approximate computations in QFT, because we still don'y know how to make the complete non-approximate computations; it could come out that virtual particles are not needed at all if we were able to make the complete computation; infact QFT actually treats quantized *fields*, not particles; it's that quantization what we usually call "particles".
What I'm having problems with is 'renormalization' :)
And that idea I've had problem since I first saw it Lightarrow:)
And now you say I will have problems with perturbation theory as well
And quantum field theory too??
Lightarrow, do you remember how dissatisfied I am with my understanding of distance:) If distance is something relating, and only relating, to 'frames' observing 'frames', what is uniform motion, speed, velocity, acceleration? And what the heck is a 'direction'?
And perhaps most importantly, what is time?
Now you know a little more why the main breakthroughs in physics happens when we understand the basic concepts better [:)].
We seem to describe things from a format where we expect numbers to come up the same, but our universe seems more likely to conform to a 'sliding standard', where things don't come up the same.
As to say that one thing is our theory about the world, and another is how the world actually is...
Like the way time seems to act in QM as compared to our macroscopic universe. When we 'renormalizes' something we expect it to behave in a accountable manner with a clear 'causality chain' showing from the least to the biggest. Now, isn't that a preconception?
Everything, always, is a preconception; nothing more than our mind's creation.
Among these mental creations, the one we call "physics" is the one which works better, that's all.
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So what do you see as 'virtual particles' Lightarrow? That is what we expect to regulate interactions at a atomic level, isn't it? So is there another idea describing them?
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Thanks, Vern. I guessed it would look contracted but I wasn't sure.
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So what do you see as 'virtual particles' Lightarrow? That is what we expect to regulate interactions at a atomic level, isn't it? So is there another idea describing them?
In quantum mechanics is difficult to 'see' anything; things become bizarre and far from ordinary experience, physics and mathematics are so linked together that you don't understand where one finish and the other begins...
What we know, or, better, the *description* we have in this moment about microscopic world is that we have fields and these fields have quantized energy. If elementary particles really exist (and not only the virtual ones) or are merely a useful way to compute things, it's not clear at all, at least to me. Have you ever asked yourself what an electron is? How big it is, how it is done?
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Oh yes, lightarrow.
And if they really are 'there' too:)
If one see time as shape filling up all of 'spacetime' moving from a 'before' towards a 'future', and you then see what we measure as being motion as instead being 'static prickings' made in 'spacetime', then we would have 'events' again :)
But the 'events' described here would not be represented of any 'sliced time slots' with 'frames' of no-time between them, instead they would consist of 'frozen static events' that 'times arrow' would create the 'motion' for, even though not really existing. And as time then would be a 'flow' we would have a 'arrow of time' constantly 'moving' creating what we call 'motion and distance'. And then those 'virtual particles' would just be a 'matter' of duration of 'pricking' and the real interest for me would be the transitions we see and try to describe, as f ex Planck length and HUP. Outlandish, isn't it :)
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Vern, quantum gravity theories (QGT) with gravitons? Shouldn't that be String theory, not QFT, in the manner that it is a theory relating to the standard model it is postulated as an idea I know, But it's still just a theory. The Standard Model doesn't, yet, include any quantum gravity, so it is not a replacement for general relativity.
As I understands it only "string theory includes a massless helicity-2 particle whose behaviour is governed by GR in the classical limit. In this sense string theory - whether or not it's correct - is our only known QGT."
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Hi yor_on; I'm having a little trouble understanding your comment. Quantum Gravity Theory would be a quantum theory. There is a string theory of gravity but I think it is different. The article I referenced was about Quantum Field Theory. QFT uses the famous Feynman diagrams to explain the force exchanges between particles.
I looked back through my posts and didn't find where I might have mixed them up; but it is possible I might have [:)]
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If you go by the predictions/expectations made from Standard Model you are correct I think. But we haven't found any gravitons and the ..QFT.. works without that it seems. String theory on the other hand seems to build on the concept of gravitons as I understands it?
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But then again:) I don't really understand string theory, it's a very esoteric subject to me.
Sorry, wrong syllables up there, QFT, not standard Model I meant.
(Time to go to sleep here I think, tomorrow I will give you a better answer Vern, hopefully so:)
Or? awh, been a very long day this one, sorry about that.
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If by esoteric you mean:
A type of hidden knowledge that is generally known only by a few individuals and not by the general public.
I think that would definitely fit string theory. I never liked string theory because I didn't see the need for it. [:)] I think Lorentz had nature pretty well nailed down back at the turn of the century. QFT, without virtual particles, would predict relativity phenomena, because without virtual particles, forces are restricted to mediation at the speed of light. This would force the Lorentz distortions we see.
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Vern you wrote "QFT, without virtual particles, would predict relativity phenomena, because without virtual particles, forces are restricted to mediation at the speed of light. This would force the Lorentz distortions we see."
Could you give me some simple example of how you think here, like A and B moving and...?
Sounds intriguing to me :)
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Okay; yor_on; here's the notion:
Set the scene to flat space-time and relativity phenomena in accord with Lorentz.
Lets imagine an atom composed of things moving in a jumble of patterns. If you like we can call these quarks and gluons and electrons. The patterns relate to each other by exchanging gluons which must move at the invariant speed of light. Now, when the atom moves, the gluons must travel a greater distance to mediate the forces. This greater amount of distance requires a greater time, and the pattern must squeeze itself together in the direction of motion, in order to remain intact.
I imagine the patterns to be in accord with my speculative Square-Of-The-Shells rule. (http://photontheory.com/Square_Shells.html) But the nature of the patterns doesn't matter, they can just as easily be the QM quark-gluon construct.
QM theory avoids predicting relativity phenomena by allowing the concept of virtual particles; since they are not confined to the natural laws they can mediate forces instantly.
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Ok Vern, I see your idea:)
Let's say that a Atom has a velocity (speed and direction) in spacetime.
If I imagine it like a 3D sphere traveling then it seems to me that the gluons movements should be equalised as they may have one 'length' moving with the 'velocity' and a equivalently shorter length if moving 'back' (depending on if it's in a uniform motion or accelerating, naturally)
So your idea can be seen as a 'deformation' of their lengths, am I right?
But how do you explain how stationary Atoms, relative Atoms traveling, also will become shorter in length, as observed from those Atoms traveling. They shouldn't be, should they? Or is it something I'm missing?
It's a interesting idea Vern.
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Have laptop, need glasses :)
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If I imagine it like a 3D sphere traveling then it seems to me that the gluons movements should be equalised as they may have one 'length' moving with the 'velocity' and a equivalently shorter length if moving 'back' (depending on if it's in a uniform motion or accelerating, naturally)
It is easier to visualize the effect if you imagine the patterns as circles flat-wise to the direction of motion. There you can easily see that the spiral is a greater distance when the pattern is moving. It is not as easy to see but you get the same effect when the circle is moving edge-wise and any angle in between.
So your idea can be seen as a 'deformation' of their lengths, am I right?
But how do you explain how stationary Atoms, relative Atoms traveling, also will become shorter in length, as observed from those Atoms traveling. They shouldn't be, should they? Or is it something I'm missing?
The atoms travelling will experience a slowing of time because a greater amount of time is required for their patterns to repeat. This will cause them to measure a lesser amount of time required to traverse a stationary object. So they would measure the stationary object as contracted in the direction of their motion.
We can't compare lengths of measuring sticks directly because we would need to bring them side by side. We can only bring them side by side when they are in the same frame of reference.
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Lorentz contraction has been mentioned a few time in threads just lately. I understand that an oblect travelling at very high speed will contract along its length in the direction of travel.
Now, GR states that if 2 objects pass each other with nothing to reference against, it is impossible for a person on 1 of them to know whether it is the object he is on or the other 1 that is moving.
So, my question is, if I was in a spaceship travelling at relativistic speed and we passed a stationary object, would it appear to me as being contracted? Surely it must to fit in with GR. But if it is velocity that causes Lorentz contraction then it wouldn't affect a stationary ship, would it?
No, it doesn't, nice thought though. No, you see, everything is relative, meaning that the effects of the Lorentz Contraction is not noticed from an inertial frame-reference, but the stationary observer will only observe the contraction. The contracion itself should not effect the observing system in any way, unless we are talking about some extreme examples, such as a relativitic-speed electron passing by a stationary atom and exhanging a gravitional fluctuation we call the graviton. In this case, then the contraction of the moving body and acceleration taking into account has caused a ''curvature'' and emits gravitional effects on another rest atom very close by, millimeters apart, for instance. But i did say it was extreme.
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Lorentz contraction has been mentioned a few time in threads just lately. I understand that an oblect travelling at very high speed will contract along its length in the direction of travel.
Now, GR states that if 2 objects pass each other with nothing to reference against, it is impossible for a person on 1 of them to know whether it is the object he is on or the other 1 that is moving.
So, my question is, if I was in a spaceship travelling at relativistic speed and we passed a stationary object, would it appear to me as being contracted? Surely it must to fit in with GR. But if it is velocity that causes Lorentz contraction then it wouldn't affect a stationary ship, would it?
LOrenz contraction was never observed, it is only a math idea
only time shrink, means clocks go slower in fast ship or stronger gravity
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LOrenz contraction was never observed, it is only a math idea
No, it's not a math idea, it's a physics fact.
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LOrenz contraction was never observed, it is only a math idea
only time shrink, means clocks go slower in fast ship or stronger gravity
Muons then?
This one first.
http://en.wikibooks.org/wiki/This_quantum_world/Appendix/Relativity/Lorentz_contraction_time_dilation
And then take a look at 'Relativistic Length Contraction' here.
http://faraday.physics.utoronto.ca/PVB/Harrison/SpecRel/Flash/LengthContract.html
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I don't think there is any question that Lorentz length contraction is a physical fact of nature. The very concept of it was forced upon us by observations that things do not behave as they should. We had to either modify our concepts of time and space or our concepts of the composition of matter to explain the observations.
Most people find it easier to modify the concept of time and space to explain relativity phenomena. I find it more satisfying to modify the concept of the composition of matter. But if the latter is the reality, it greatly reduces the options of the true nature of the universe. If space-time is flat, the universe can't be expanding. If matter is simply electromagnetic change, black holes can not exist. And many more.
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Lorentz contraction exist only as a math idea
nothing contract when moving
only time contract, this means that clocks run slower by moving faster
time is run of clocks
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Lorentz contraction exist only as a math idea
nothing contract when moving
only time contract, this means that clocks run slower by moving faster
time is run of clocks
Not only do we know that Lorentz contraction does actually happen. We know why it happens. Why do you suppose that it does not happen? Can you cite any physical phenomena that suggests that Lorentz contraction does not happen?